Rechargeable, all-solid state Li-ion batteries (LIBs) with high specific capacity and small footprint are highly desirable to power an emerging class of miniature, autonomous microsystems that operate without a hardwire for power or communications. A variety of three-dimensional (3D) LIB architectures that maximize areal energy density have been proposed to address this need. The success of all of these designs depends on an ultra-thin, conformal electrolyte layer to electrically isolate the anode and cathode while allowing Li-ions to pass through. However, as we demonstrate in our Letter, a substantial reduction in the electrolyte thickness can lead to rapid self-discharge of the battery even when the electrolyte layer is conformal and pinhole-free. We demonstrate this by fabricating individual, solid-state nanowire core-multishell LIBs (NWLIBs) and cycling these inside a transmission electron microscope. For nanobatteries with the thinnest electrolyte, ≈110 nm, we observe rapid self-discharge, along with void formation at the electrode/electrolyte interface, indicating electrical and chemical breakdown. With electrolyte thickness increased to 180 nm the self-discharge rate is reduced substantially and the NWLIBs maintain a potential above 2 V for over 2 h. Analysis of the nanobatteries electrical characteristics reveals space-charge limited electronic conduction, which effectively shorts the anode and cathode electrodes. Our study illustrates that at reduced dimensions the increase in the electric field can lead to large electronic current in the electrolyte effectively shorting the battery. The scaling of this phenomenon provides useful guidelines for design of 3D LIBs.
Citation: Nano Letters
Pub Type: Journals
Lithium ion battery, nanowire, nanobattery, in situ transmission electron microscopy, electrolyte, breakdown, space-charge limited conduction.